1. Field of the Invention
This invention relates generally to computer hard disk drive actuator assemblies and, more particularly, to the design and manufacturing process of fiber composite actuator assemblies.
2. Description of Related Art
Magnetic disk drives are information storage devices that utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a magnetic recording head or transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer in proximity to the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and for maintaining the transducer over the data track center line during a read or a write operation. The magnetic media disk or disks in the disk drive are mounted to a spindle. The spindle is attached to a spindle motor, which rotates the spindle and the disks to provide read/write access to the various portions on the concentric tracks on the disks.
The actuator positions the transducer over the correct track according to the data desired on a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled to position the transducer over the desired data track by shifting the combination assembly across the surface of the disk in a direction generally transverse to the data tracks. The actuator may include a single positioner arm extending from a pivot point, or alternatively, a plurality of positioner arms arranged in a comb-like fashion extending from a pivot point, sometimes referred to as an xe2x80x9cE-block.xe2x80x9d A rotary voice coil motor (VCM) is attached to the rear portion of the actuator assembly to power movement of the actuator over the disks.
During operation of the disk drive, the actuator is positioned radially over the disk surface under the control of a positioning servo system. The servo system is designed to accurately position the read/write transducer over a selected data track on the disk in as short a time as possible and to maintain the read/write transducer position over the data track as accurately as possible. As data storage density of disk drives increases, the radial density of data tracks on the disk increases. The ability of the servo system to accurately track on the resulting narrower data tracks becomes a limitation on the disk drive performance.
Actuator assemblies have resonant frequencies that can adversely affect the performance of the servo system. Low frequency resonances severely limit the bandwidth of the servo system, resulting in poor high frequency response and degraded disk drive performance. In addition, fast access to the information stored on the disks requires a low inertia positioner with a short settling time and good damping characteristics after positioning. So, with a fast servo for positioning, the positioner should be constructed to have high resonant frequencies with good signal following properties and a short response time.
A number of low density, high stiffness composites are available, which offer low inertia and ease of manufacturability compared to traditional aluminum, magnesium, or stainless steel actuator arms. The most common material used to overmold an actuator body around metal arms is a liquid crystal polymer filled with up to 30% short carbon fibers (see U.S. Pat. No. 5,656,877). This material, or a similar polymer composite, can be used for molding individual actuator arms (see IBM TDB Vol. 31, No. 10). The limitations of this liquid crystal polymer, when compared to traditional metals, include its poor stiffness and strength. This occurs because of (1) the low volume percentage (20-30%) of fiber, (2) fiber misalignment to the principal stress direction, and (3) the short fiber length. Although a number of composite materials are stiffer than the pure polymer matrix, they do not have sufficient stiffness to achieve the actuator design goal of a greater bandwidth of the servo system required for high tpi (track per inch) hard disk drives.
Recent constructions of an E-block have included a monolithic body, with integral positioning arms and integral carrier arms. A common method to manufacture a monolithic E-block is to bond together unidirectional fiber mats to form a thick laminate block. To achieve the desired E-block geometry, the laminate block is then machined. Machining away 50 to 70 percent of the carbon fiber composite block to create the actuator E-block produces a significant amount of scrap.
Another method to manufacture an E-block involves cutting a unidirectional fiber sheet to produce an individual arm for a stacked actuator configuration. By using this method, arm strength is severely compromised as a result of (1) cutting fibers to make a taper shaped arm, and (2) creating areas of weakness prone to cracking at the bearing bore hole and tooling holes as the axes of short fibers are oriented with the direction of bending. Stamping an arm out of a sheet of unidirectional fiber composite is risky because the thin arm ( less than 1 mm) will easily crack along its long axis in the direction of the grain.
In Japanese Patent Publication JP 408315520A, the actuator is formed out of a fiber composite material, especially a carbon/carbon-based three-dimensional continuous fiber type composite material, which is also cut at its edges.
The weakening effect of cutting fibers is further illustrated in Japanese Patent Publication JP 2081377, which discloses winding around a pin fibers that have been treated with thermal hardening resin, after which they are cut to shape in the form of a HDD (hard disk drive) load beam. The cut edges are subsequently sealed in a secondary operation. The other cases without this additional step will generate exposed cut carbon fiber particles that will shed off of the E-block. When these fragments of carbon fiber become airborne, the disk drive""s air turbulence allows them to migrate to the head-disk-interface, where they will cause data to be lost by initiating a head crash.
In Japanese Patent Publication JP 6-68481, carbon fiber composite carriage mechanisms for optical heads are manufactured by lay-up of prepreg woven mats of the fibers aligned in more than one direction. Although the fiber orientation is aligned in the respective layers with the direction of the torsion and bending stresses, stiffness is still compromised because of: (1) volumetric inefficiencies of woven mats, (2) material anisotropy of woven mats, and (3) reduced volumetric fraction of carbon fibers due to the layers of polymer separating the mats.
The low stiffness and strength of woven composites can be improved by using a unidirectional fiber direction. Unidirectional fiber mats typically have a 70 percent packing density, which is unachievable in woven mats. Despite this gain/improvement, unidirectional fiber composites are weak and compliant in the direction perpendicular to the fiber orientation. In addition, when laying up unidirectional fibers, it is difficult to achieve good fiber continuity throughout a part that has holes, that is non-rectangular, and that has complex three-dimensional geometry. Thus, the previous methods of manufacturing E-blocks are not desirable.
Designs have incorporated carbon fiber inserts to stiffen weak E-block arms. In one design (WO 96/07181), metal E-block arms are stiffened by adhesively bonding a U-channel shaped, fiber-reinforced composite preform to the edge of the arm. The increased thickness of the arm, which must fit within a tight disk-to-disk limitation, is clearly a disadvantage. Compact construction of the device requires minimal disk separation between the stacked disks.
It is therefore desirable to create a low density, low inertia composite actuator that has improved stiffness, strength and high damping characteristics, and overcomes the drawbacks in the prior art.
To overcome the shortcomings of the prior art described above, it is an object of the present invention to provide a near net shape fiber composite actuator assembly that requires little to no secondary finishing operations such as cutting or machining of the fiber structure to form the periphery of the assembly. It is another object of the present invention to provide an actuator assembly such as an E-block that is made of a composite material that is low in density and high in mechanical strength and stiffness, and relatively less costly to manufacture. It is another object of the present invention to provide a method of manufacturing (including winding) disk drive actuator components such as an E-block, of a fiber reinforced metal matrix composite or polymer matrix composite.
In one aspect of the present invention, to maximize the material""s mechanical stiffness and strength, fibers are continuously wound to form the fiber composite actuator components. More specifically, fibers are wound substantially continuously in a direction along the periphery of the actuator component. This results in fibers orientated generally in the longitudinal direction of the component, and in a direction along the periphery of the matrix of the component, with fibers bending around all large radii to provide fiber continuity around the component""s perimeter. Longitudinal fiber orientation and the higher fiber packing density, which can be easily achieved by winding, maximize both the in-plane bending stiffness (or sway mode stiffness) and the out-of-plane bending stiffness of an elongated member. Continuous winding also solves the lengthwise cracking problem associated with cutting. These advantages were not accomplished with laminated composites disclosed in the prior art.
In one embodiment of the present invention, an actuator positioner arm is made of a fiber composite material comprising continuous fiber windings in accordance with the present invention. In another embodiment of the present invention, an E-block is made by stacking actuator arm components that are individually formed by continuous fiber windings in accordance with the present invention. In another embodiment of the present invention, a dual-purpose wound-form is deployed to facilitate the winding process, which will become an integral part of the final actuator assembly structure. In yet another embodiment of the present invention, certain preformed actuator components such as coils and pivot bearing are used as mandrels to facilitate fiber windings, which will become integrated into the final actuator assembly in the winding process.
In another aspect of the present invention, at the end of the fiber winding process, the fiber wound actuator assembly is applied as a preform, and further combined with a metal or polymer matrix to complete an E-block having fiber-reinforced metal or polymer matrix.
The above, as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.